A major deficiency of compression molded thermoset (cured) glass fiber reinforced polyester (FRP) moldings is surface imperfections such as pits, pores, surface cracks, waviness and sink marks requiring substantial post-curing handling such as sanding, filling and so forth requiring considerable expense in additional materials and labor. The in-mold coating process of U.S. Pat. No. 4,081,578 masks these imperfections by molding a low viscosity thermosetting composition onto the surface of the thermoset FRP part in a second molding operation. The resulting skin or thin adherent thermoset coating, however, experiences about an 8% volume shrinkage on curing although pits, pores, cracks, waviness and sink marks are generally eliminated. In the case of pits slight dimples in the coating at those locations sometimes remain. The shrinkage is due to polymerization and/or crosslinking and also due to thermal effects caused by cooling.
It is an object of the present invention to avoid the difficulties alluded to hereinabove and to provide an in-mold coating thermosetting composition which exhibits a reduced amount of or no shrinkage on molding and curing.
Another object of the present invention is to provide a thermoset polyester glass fiber reinforced part with an in-mold molded adherent thermoset coating which exhibits a reduced amount of or no shrinkage.
These and other objects and advantages of the present invention will become more apparent to those skilled in the art from the following detailed description and working examples.